Saudi Arabia has identified 18 new cases of Middle East Respiratory Syndrome (Mers), it said late on Wednesday, pushing the total number of infections in the country so far to 449.

Four people died from the disease on Wednesday, taking the total death toll in Saudi Arabia to 121 since Mers, a form of coronavirus, was identified two years ago, the Health Ministry said in a statement on its website.

The rate of infection in Saudi Arabia has surged in recent weeks after big outbreaks associated with hospitals in Jeddah and Riyadh. The total number of infections nearly doubled in April and has risen by a further 21 per cent already in May.

The World Health Organisation said on Wednesday the hospital outbreaks had been partly due to “breaches” in recommended infection prevention and control measures, but added that there was no evidence of a change in the virus’s ability to spread.

Scientists around the world have been searching for the animal source, or reservoir, of Mers virus infections ever since the first human cases were confirmed in September 2012.

Eight of the new cases were in Jeddah, five in the capital Riyadh, one in Najran. There were three new cases in Madinah and one in Makkah, two cities that receive large influxes of Muslim pilgrims from around the country and overseas.

Half of them were in contact with people who had previously been diagnosed as having Mers, the ministry said.